There are a number of health-related applications that benefit from knowledge (e.g., periodic and/or constant monitoring of) of core body temperature. Generally, the external temperature of a human body can differ from the temperature of internal tissues of a human body by as much as 2.5 degrees Kelvin, and can also vary during the day (e.g., as a natural physiological process, in relation to exercise, in relation to eating, etc.). A number of disorders can cause this temperature difference can vary from that in a healthy body. For example, athletes, soldiers, firefighters and other professions working in extreme conditions or under heavy exertion can experience exertional hyperthermia. Such hyperthermia can result in fatigue, heat-related illness, and even death. Cancer cells can have increased temperatures, as can inflamed tissues, such as those in joints of arthritis patients. Sleeping disorders are accompanied by changes in the circadian cycle, which can also be related to changes in phase and amplitude of periodic variations in core body temperature. Infants suffering from hypoxia-ischemia have an elevated brain temperature; and, if detected, can be effectively treated.
Thus, internal temperature monitoring can be used in various diagnostics applications, for example, as an indication of one or more disorders or conditions. Further, some treatments for such disorders and conditions (e.g. in hyperthermia for cancer treatment) can be aided by internal temperature monitoring. A number of techniques exist for monitoring core body temperature. Most conventional techniques tend to involve invasive methods, such as rectal probes, gastro-intestinal sensors, surgically inserted thermometers, etc. Some other conventional techniques are less invasive or non-invasive. For example, some approaches use zero-heat-flux sensing techniques. However, it has been generally accepted that no non-invasive methods are currently considered acceptable for diagnosing heat-related illness.